Along an assembly line, various types of articles, such as for example, diapers and other absorbent articles, may be assembled by adding components to and/or otherwise modifying an advancing, continuous web of material. For example, in some processes, advancing webs of material are combined with other advancing webs of material. In other examples, individual components created from advancing webs of material are combined with advancing webs of material, which in turn, are then combined with other advancing webs of material. In some cases, individual components created from advancing web or webs are combined with other individual components created from other advancing web or webs. Webs of material and component parts used to manufacture diapers may include: backsheets, topsheets, leg cuffs, waist bands, absorbent core components, front and/or back ears, fastening components, and various types of elastic webs and components such as leg elastics, barrier leg cuff elastics, stretch side panels, and waist elastics. Once the desired component parts are assembled, the advancing web(s) and component parts are subjected to a final knife cut to separate the web(s) into discrete diapers or other absorbent articles.
During the assembly process, various components and/or advancing webs of material may be bonded together in various ways. For example, in some processes, advancing webs and/or components may be bonded together with adhesives. In other processes, advancing webs and/or components may be mechanically bonded together with heat and pressure without the use of adhesives. An example of such a mechanical bonding method and apparatus is disclosed in U.S. Pat. No. 4,854,984, wherein two laminae are bonded together by advancing through a nip between a patterned cylinder and an anvil cylinder. Pattern elements on the patterned cylinder exert pressure on the two laminae against the anvil roll to create discrete bond sites. More particularly, bond sites are created as the extreme nip pressure compresses and yields the laminae material in areas between the pattern elements and the anvil. During the bonding process, some of the yielded material may flow from the bond site to areas surrounding the perimeter of the pattern element.
However, extreme nip pressures may exceed the compressive yield strength of cold work powder metal tool steels. In addition, current mechanical bonding methods are susceptible to pattern element chipping, spalling, buckling, and/or otherwise fracturing, referred to generally as bond tool breakdown, sometimes necessitating frequent and costly repairs. These mechanical bonding methods may also damage the laminae by forming holes and/or tears in or around the bond sites. For example, pattern elements may become deformed and/or fail after prolonged use due to high stresses that occur in the center portions of the pattern element during the bonding operation. In some instances, such high stresses may cause craters to form in the bonding surfaces of pattern elements. As a pattern element degrades, the bonds created thereby may have inconsistent aesthetic appearances; have relatively weaker strengths; and may tear or cut the bonded laminae in areas adjacent to the bonds. In addition, as the web basis weight of laminae decreases, bonds may become more susceptible to bond defects such as tearing and pinholes at relatively high nip pressures.
Consequently, it would be beneficial to provide a method and apparatus for mechanically bonding substrates that produces bond sites with relatively low damage to the laminae and with reduced bond tool breakdown.